| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Dan Ports <drkp(at)csail(dot)mit(dot)edu>, Florian Pflug <fgp(at)phlo(dot)org>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: SSI and Hot Standby |
| Date: | 2011-01-21 09:19:25 |
| Message-ID: | 4D394F9D.6020207@enterprisedb.com |
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| Lists: | pgsql-hackers |
On 21.01.2011 11:10, Simon Riggs wrote:
> So any xid that commits in a different sequence to the order in which
> the xid was assigned creates a potential for unserialization? Or?
It's not the order in which the xid was assigned that matters, but the
order the transactions started and got their snapshots. The xids might
be assigned a lot later, after the transactions have already read data.
> On HS we know the order of arrival of xids, and we know the order of
> commits, so we should be able to work out which are the potentially
> unserializable snapshots. That would allow us to make the standby
> independent of the master, thereby avoiding all this messy information
> flow.
Unfortunately although we know the order of arrival of xids, it doesn't
tell us the order the transactions started.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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